It is known to use sulfur-containing organosilicon compounds, such as 3-mercaptopropyltrimethoxysilane, 3-thiocyanatopropyltriethoxysilane or bis(3-{triethoxysilyl}propyl)tetrasulfane, as silane coupling agents or reinforcing additives in oxide-filled rubber mixtures, inter alia for the production of treads and other parts of automobile tires (DE 2 141 159, DE 2 212 239, DE 195 444 69 A1, U.S. Pat. Nos. 3,978,103, 4,048,206, EP 784 072 A1).
The additional use of alkylsilanes in rubber mixtures to reduce the mixing viscosity is also known (EP 795 577 A1, EP 864 605 A2).
In the preparation of rubber mixtures with organosilanes and a filler, for example a precipitated silicic acid, a chemical reaction takes place during the mixing process, for example in an internal mixer. This chemical reaction is a condensation reaction which is accompanied by the release of a considerable amount of alcohol. As described in the literature [A. Hunsche, U. Görl, A. Müller, M. Knaack, T. Göbel, Kautsch. Gummi, Kunstst. 50, 881 (1997)], this condensation reaction is made up of a primary reaction, in which an ethoxy group reacts with a silanol group from the silicic acid, and a secondary reaction between two ethoxy groups, which results in crosslinking between the silane molecules. According to the state of the art, up to three mol of ethanol can be eliminated per mol of silicon by these reactions when silanes containing three ethoxy functional groups are used.
In some cases this eliminated alcohol causes appreciable technical problems in the further processing of the rubber mixtures, such as the porosity of the mixture during extrusion or undesired blistering in the rubber itself. Furthermore, it is in the interest of health and the environment to reduce the amount of alcohol released during the reaction.